Plastic lens, manufacturing method thereof, production tracing management method thereof, and optical pickup device

ABSTRACT

A lens has a flange part at the outer periphery of its surface. A flange surface of the flange part is higher than the lens surface. The flange surface has a marking to identify a production jig, for example.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present invention is related to Japanese Patent ApplicationSerial No. 2002-342775, which is hereby incorporated.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a plastic lens used in opticalelements such as cameras and optical disc apparatus, a manufacturingmethod of the same, a production tracing management method for a plasticlens, and an optical pickup device having a plastic lens.

[0004] 2. Description of the Related Art

[0005] Digital cameras and optical disc apparatus have been spread. Theoptical disc apparatus, for example, have an optical pickup device forreading information stored on an optical storage medium. The opticalpickup device has a pickup lens for focusing light from a light sourceon the optical storage medium.

[0006] The pickup lens is generally manufactured by molding glass orplastic such as polyolefin resin or acrylic resin. A plastic pickup lensis produced by injection molding, transfer molding, or other moldingtechniques using a mold. In an injection molding process, for example,resin is poured into a cavity in the mold through a gate and allows itto cool to solidify, thereby producing a pickup lens.

[0007] This kind of plastic lenses are mass-produced to reduce unitprice. Thus, a plurality of lenses are simultaneously produced using amold having a plurality of cavities. For example, eight lenses areproduced at a time using a mold having eight cavities. Though thequality of the lens formed in each cavity is preferably the same, it mayvary in practice. Further, the quality may vary by mold and moldingdevice.

[0008] A technique of marking a plastic lens is disclosed in JapaneseUnexamined Patent Application Publication No. 2002-122711, and UnitedStates Patent Application Publication No. 2001/0017733, Asakura, forexample. To distinguish a lens surface, this technique deposits acoating film that serves as a marking on the peripheral area of one lenssurface by printing, coating, or evaporation. Thus, the material of thelens and the marking are different; therefore, this technique furtherrequires a marking process in addition to a lens molding process whenproducing a lens by injection molding.

[0009] Another marking technique for another object is disclosed inJapanese Unexamined Patent Application Publication No. 2000-111709. Thistechnique creates a convexity or concavity on a flange surface of anoptical component to indicate a resin injection position. No mention ismade to a manufacturing method nor mold used in this technique. Sincethe convexity or concavity is placed on the upper surface of the flangepart, however, the marking is likely to chip away or get contaminatedwhen put on a desk or by handling. This causes to fail to convey markinginformation properly. Besides, the whole purpose of the markingdescribed in this technique is to align the position of a gate, not toidentify a lens nor track the production of the lens during theproduction process. This is obvious from the fact that the marking isformed only in one place, thus unable to distinguish between a pluralityof lenses. In addition, the convex marking in the structure shown inFIG. 5 of the publication projects above the upper flange surface by 0.1to 0.5 mm. Thus, the lens is unstable when placed with the surfacehaving the convex marking facing down. Further, the convex marking canchip away by contact with another component. The concavity formed at theupper flange surface, on the other side, is likely to suffer fromaccumulation of contamination, for example glue, which reducesvisibility. It is therefore preferred that the marking is visible evenif it is formed at the other portion than the flange surface, and itdoes not touch another component. These references are incorporatedherein.

[0010] As described earlier, the quality of lenses produced by moldingmay vary by mold or cavity. This raises the need for quality control,production management, and production tracing of a lens after mounted onan optical device. It is thus preferred to create a marking on a lensitself to identify a production jig such as a mold and a cavity or aproduction line process. The creation of the marking, however, shouldnot deteriorate the performance of the lens. The lens is an opticalcomponent, and certain performance is required accordingly. Creating themarking on an optical functional part at the center of the lens, forexample, should be avoided since this has an adverse effect on theoptical function.

[0011] Further, if a marking is broken by abrasion with anothercomponent, it not only reduces visibility of the marking, but alsodeteriorates the optical performance of the optical functional part dueto a broken dust attached thereto.

SUMMARY OF THE INVENTION

[0012] An object of the present invention is to provide a plastic lenshaving a marking optimally created thereon, an optical pickup device,and a manufacturing and production management method of the lenssuitable for integrally molding such a marking by injection molding.

[0013] To these ends, according to the present invention, there isprovided a plastic lens produced by injection molding of resin material,including a flange part on a periphery of a lens surface, a flangesurface on at least one side of the flange part having a part higherthan the lens surface and a depressed part formed on at least a partthereof; and a marking integrally molded by injection molding to amarking surface of the depressed part, a highest point of the markingbeing lower than a highest point of the flange surface.

[0014] Preferably, the flange part has a cutout portion in an outer sidesurface thereof. Further, the flange surface is preferablymirror-finished at least in a vicinity of an area where the marking isformed.

[0015] According to the present invention, there is provided a plasticlens produced by injection molding of resin material, including a flangepart on a periphery of a lens surface, a flange surface on at least oneside of the flange part having a part higher than the lens surface; anda marking integrally molded to the flange surface by injection molding,for identifying a production jig used to produce the lens.

[0016] Preferably, a highest point of the marking is lower than ahighest point of the flange surface. The marking is preferably formed ina depressed part of the flange surface. Further, it is preferred thatthe flange part has a cutout portion in an outer side surface thereof.The flange surface is preferably mirror-finished at least in a vicinityof an area where the marking is formed.

[0017] According to the present invention, there is provided an opticalpickup device having the above described lens.

[0018] According to the present invention, there is provided a method ofmanufacturing a plastic lens produced by injection molding of resinmaterial in a mold cavity, the lens having a marking on a different partfrom an optical functional part. The method includes the steps ofproviding a mold part for one side comprising a first mold member and asecond mold member, the first mold member and the second mold memberforming a part of the mold cavity; providing a mold part for other sideto form the mold cavity cooperable with the mold part for one side whenassembled; injecting resin material into the mold cavity; forming theoptical functional part of one side of the lens, with the first moldmember; and forming the different part of one side of the lens than theoptical functional part and the marking thereon, with the second moldmember.

[0019] Preferably, the different part of one side of the lens than theoptical functional part has a flange part on a periphery of a lenssurface. A boundary between the first mold member and the second moldmember is preferably located near an innermost periphery of the flangepart of the lens. The flange part of the lens preferably has a depressedpart on at least a part thereof and a marking integrally molded to thedepressed part by injection molding. Further, it is preferred that theflange part of the lens includes a flange surface on at least one sideof the flange part having a part higher than the lens surface and adepressed part on at least a part thereof, and a marking integrallymolded by injection molding to a marking surface of the depressed part,a highest point of the marking being lower than a highest point of theflange surface. Furthermore, the flange surface preferably has a cutoutportion in an outer side surface thereof. The flange surface of theflange part is desirably mirror-finished at least in a vicinity of anarea where the marking is formed.

[0020] According to the present invention, there is provided a method oftracing production of a plastic lens produced by injection molding ofresin material. The method includes the step of manufacturing theplastic lens comprising a flange part on a periphery of a lens surface,a flange surface on at least one side of the flange part having a parthigher than the lens surface, and a marking integrally molded to theflange surface by injection molding; and the step of tracing productionof the lens by use of the marking formed on the lens.

[0021] According to the present invention, there is provided anothermethod of tracing production of a plastic lens produced by injectionmolding of resin material. The method includes the step of manufacturingthe plastic lens comprising a flange part on a periphery of a lenssurface, a flange surface on at least one side of the flange part havinga part higher than the lens surface, and a marking integrally molded tothe flange surface by injection molding, a highest point of the markingbeing lower than a highest point of the flange surface; and the step oftracing production of the lens by use of the marking formed on the lens.

[0022] Preferably, each position of the marking formed on each lens iscircumferentially different on the flange surface to distinguishproduction of one lens from another. Further, it is preferred that eachshape of the marking formed on each lens is different to distinguishproduction of one lens from another.

[0023] According to the present invention, there is provided a mold formanufacturing a plastic lens produced by injection molding of resinmaterial and having a marking on a part different from an optical isfunctional part. A mold at a side where a marking will be formedincludes a first mold member to form an optical functional part of oneside of the lens, and a second mold member to form a part different fromthe optical functional part of one side of the lens. The second moldmember is separatable from the first mold member and has a portion toform the marking.

[0024] The present invention can provide a lens where a marking forproduction tracing is created in the most effective way, a manufacturingmethod thereof, and an optical pickup device.

[0025] The above and other objects, features and advantages of thepresent invention will become more fully understood from the detaileddescription given hereinbelow and the accompanying drawings which aregiven by way of illustration only, and thus are not to be considered aslimiting the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIGS. 1A and 1B are a top plan view and a side plan view,respectively, of a lens according to the present invention.

[0027]FIG. 2 is an enlarged sectional view of a flange part of a lensaccording to the present invention.

[0028]FIG. 3 is an enlarged sectional view of a flange part of a lensaccording to the present invention.

[0029]FIG. 4 is an enlarged sectional view of a flange part of a lensaccording to the present invention.

[0030]FIG. 5 is an enlarged sectional view of a flange part of a lensaccording to the present invention.

[0031]FIGS. 6A and 6B are a top plan view and a side plan view,respectively, of a lens according to the present invention.

[0032]FIG. 7 is a sectional view showing production of a lens accordingto the present invention.

[0033]FIGS. 8A and 8B are sectional views showing production of a lensaccording to the present invention.

[0034]FIG. 9 is a view showing an optical pickup device according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Embodiment 1

[0036] A lens according to the first embodiment of the present inventionwill be explained hereinafter, taking a pickup lens as an example, withreference to FIGS. 1A, 1B, and 2.

[0037]FIG. 1A is a top plan view of a lens 1. FIG. 1B is a side planview of the lens 1, and the left half shows a cross-section of the lens.As shown therein, a flange part 2 is formed on the outer periphery ofthe lens 1. The flange part 2 has an upper flange surface 21, whichfaces toward an optical recording medium when the lens 1 is mounted onan optical disc apparatus to read information from the optical recordingmedium. The other side is a lower flange surface 23. The flange part 2,which is strip-shaped, is placed on the entire periphery of an opticalfunctional part of the lens 1. The flange part 2 is not necessarilycompletely around the periphery, and it may have a notch at a part ofthe periphery.

[0038] As shown in FIG. 1B, the highest part of the upper flange surface21 is higher than the upper surface of the optical functional part inthe optical axis direction. Thus, when the lens 1 is placed on a desk orso on with the upper flange surface 21 facing down, the upper flangesurface 21, not the optical functional part, touches the desk. Thisprevents the optical functional part from being damaged by contact witha desk and the like. This also prevents it from being damaged by directcontact with an optical recording medium after the lens 1 is mounted toan optical disc apparatus.

[0039] The lens 1 in this example has a diameter of 5.8 mm, includingthe flange part 2. The flange part 2 has a vertical width of 0.9 mm. Alens in another example has a diameter of 3.8 mm.

[0040] As shown in FIG. 1A, the upper flange surface has a depressedpart 20. Markings 3 a and 3 b are created in two different positions onthe depressed part 20. The markings are used to identify a productionjig such as a mold, a cavity, or an injection molder. The markings 3 aand 3 b are formed not to be higher than the highest part of the upperflange surface 21. The markings 3 a and 3 b are integrally molded to theupper flange surface 21 by providing a mold for the surface with theshapes corresponding to the markings. The markings are placed in twodifferent positions to distinguish lenses produced with differentproduction jigs by changing their relative positions. A cavity, forexample, is distinguishable by changing the relative positions of themarkings according to a cavity. Specifically, for the first cavity, themarkings are placed in such positions that the angle between the linesconnecting the center of the lens to each of the markings is 180degrees. For the second cavity, on the other hand, the markings areplaced in circumferentially different positions in which the above angleis 120 degrees.

[0041] The markings 3 a and 3 b each have a shape of half-round convex.Though a concave shape can also serve as a marking, the convex shape ispreferable because of ease of mold production. The markings 3 a and 3 bin this example have a height of 0.02 to 0.03 mm. The half-round convexshaped markings is advantageous in that mold production is easy. Theshape of the marking 3 is not necessarily half-round, and it maybeanother shape such as a square or a cross, or it may be a shape of aletter such as an alphabet or a number. Though the markings 3 a and 3 bhave the same shape in this example, they may have a different shape.The number of the markings 3 may be more than two. Or, it may be one ifthe shape varies by unit to identify such as by cavity. Further, if thelens has a marking indicating the position of a gate, checking therelative position of this marking and the marking 3 allowsidentification. Furthermore, one lens may have markings for identifyingboth a mold and a cavity. For example, the marking for identifying amold may be two parallel convexities, while the marking for identifyinga cavity may be one convexity, thereby distinguishing between the two.

[0042]FIG. 2 is an enlarged sectional view of the flange part 2 of thelens 1. If the marking 3 is placed on the highest part of the upperflange surface 21 in the optical axis direction, the fine marking 3 maybe broken to be invisible by abrasion with the surface where the lens isplaced during the production process or by contact with an opticalrecording medium when the lens 1 is mounted to an optical pickup device.Further, if the marking 3 is chipped away, it may generate plasticparticles or dust, which causes a problem. A solution to the aboveproblems is to create a depressed part 20 on at least a part of theflange surface, and form the marking 3 thereon to be lower than thehighest part of the upper flange surface 21. In this embodiment, theflange surface has a depressed part 20 formed in the circumferentialdirection, and the marking 3 is placed on the depressed part 20 so thatit is lower than the highest part of the upper flange surface 21. Havingthe marking 3 not protruding above the upper flange surface 21, thisembodiment can reduce the risk of damage by abrasion.

[0043] In the upper flange surface 21, the surface of the depressed part20 where the marking 3 b is formed is a marking surface 211. The markingsurface 211 is lower than the flange surface 21 in the optical axisdirection. For easier release of a molded product from a mold, themarking surface 211 is lower than the highest point of the upper flangesurface 21 preferably by less than 100 μm, and more preferably by 50 μmand less. The marking surface 211 may be higher or lower than the lenssurface.

[0044] The upper flange surface 21 including the marking surface 211 ismirror-finished in a polishing process of a mold member. Since a surfacewith a mirror finish has higher reflectivity than a surface without amirror finish, the bright and dark contrast is great between the marking3 and the other part. There is thus an advantage of the increasedvisibility of the marking 3. The mirror finish may be applied to thewhole area of the upper flange surface 21 or to a limited area in thevicinity of the marking. When creating a marking on the marking surface211, the ratio M/W of the width (M) of the bottom of the marking and thewidth (W) of the marking surface is preferably 2 to 10, and morepreferably 2.5 to 5.

[0045] Preferably, the marking surface 211 does not extend to the outerperipheral part of the lens by forming the highest portion in the flangesurface at the outer peripheral part of the marking surface 211. Thisprevents an adhesive from flowing thereinto to make the markinginvisible.

[0046] Another solution to the problem of damage by abrasion is to placethe marking 3 not on the upper flange surface 21 but on the other partoutside of the optical functional part, for example, the outermostperipheral area of the lens surface. However, this has the problem thatthe marking 3 is blocked from view by the flange part 2. In addition, tohave a large effective diameter or optical functional part, it is notpreferred to place the marking 3 on the lens surface. The presentembodiment thus places the marking 3 on the flange part 2. Since themarking 3 is placed on the upper flange surface 21 in this embodiment,the marking 3 is still visible after the lens 1 is attached to anoptical disk apparatus.

[0047] In this embodiment, the lowest point of the upper lens surfaceand the highest point of the lower lens surface are not in correspondingpositions as shown in FIG. 2. A boundary Q between the lower flangesurface 23 and the lens surface is located at the outer side of aboundary P between the upper flange surface 21 and the lens surface.This ensures the marking surface to still have a sufficient width whenthe thickness of the lens is reduced and that of the flange part isreduced accordingly.

[0048] Embodiment 2

[0049] A lens according to the second embodiment of this invention isdifferent from the lens according to the first embodiment in the shapeof the flange part. Other aspects are the same as the first embodiment,and therefore same explanation will be shortened.

[0050]FIG. 3 is an enlarged sectional view of the flange part of thelens in the second embodiment of the invention. As shown therein, theflange surface has a depressed part, and the bottom surface of thedepressed part is a marking surface 211. The marking surface 211 islower than the upper flange surface 21. The marking surface 211 extendsto the inner periphery of the flange part. It is also possible that theupper flange surface 21 lies on both the outer periphery and the innerperiphery of the flange part with the marking surface 211 lyingtherebetween, as shown in FIG. 3. The height of the upper flange surface21 at the outer and inner periphery is not necessarily equal.

[0051] The upper flange surface 21 is preferably perpendicular to theoptical axis direction; however, the surface may be inclined.

[0052] In the following, a process of manufacturing the lens having theabove configuration by injection molding will be briefly explained.

[0053] The process begins with creation of a mold. The mold has a shapecorresponding to the shape of an article to be produced. The mold usedin this embodiment has such a shape as to form a marking on the upperflange surface 21.

[0054] The next is setup of the mold in an injection molder. Then, inthe injection molder, resin is injected into a cavity in the moldthrough a gate. The resin in the cavity then cools to solidify. A lensis thereby produced.

[0055] As described above, the lens according to this embodiment has themarking created in the most effective manner to identify a productionjig such as a cavity and a mold. This provides the same advantage as thelens according to first embodiment.

[0056] Embodiment 3

[0057] A lens according to the third embodiment of this invention isdifferent from the lens according to the first embodiment in theposition of the marking. Other aspects are the same as the firstembodiment, and therefore same explanation will be shorten.

[0058]FIG. 4 is an enlarged sectional view of the flange part of thelens according to the third embodiment. As shown therein, the marking 3b, which is a half-round convex shape, is created on the upper flangesurface 21. The marking 3 b is formed to be lower than the highest partof the upper flange surface 21. In the lens according to thisembodiment, the depressed part 20 is formed at the outer part of theupper flange surface 21.

[0059] As described above, the lens according to the third embodiment ofthis invention has the marking created in the most effective manner toidentify a production jig such as a cavity and a mold. It provides thesame advantage as the lens according to above embodiments.

[0060] Embodiment 4

[0061] A lens according to the fourth embodiment of this invention isdifferent from the lens according to the first embodiment in the shapeof the outer side surface of the flange part. Other aspects are the sameas the first embodiment, and therefore same explanation will beshortened.

[0062]FIG. 5 is an enlarged sectional view of the flange part of thelens in the fourth embodiment. The lens is attached to a pickup holder 4of an optical pickup device. As shown therein, the flange part 2 of thelens has a cutout portion 221 at its outer side surface. The cutoutportion 221 has such a shape that the upper part of the outer sidesurface of the flange part 2 is cut away. Though the cutout portion 221is provided on the entire periphery of the flange part 2 in thisexample, it is not necessarily on the entire periphery.

[0063] A pickup holder 4 holds the lens by the lower flange surface 23and a side flange surface 22. Specifically, the pickup holder 4 has amounting portion 41 where the lower flange surface 23 is placed and aprotruding portion 42 projecting upward at the outer side of themounting portion 41.

[0064] The bottom surface of the cutout portion 221 is at substantiallythe same height as the top surface of the protruding portion 42 of thepickup holder 4. In other words, the height H of the protruding portion42 is substantially the same as the distance between the bottom surfaceof the cutout portion 221 and the lower flange surface 23.

[0065] The lens 1 is attached to the pickup holder 4 generally with anadhesive. The cutout portion 221 serves as an adhesive reservoir. Thisprevents that an adhesive flows into the area of the marking 3 b to makethe marking 3 b invisible.

[0066] Embodiment 5

[0067] A lens according to the fifth embodiment of this invention isdifferent from the lens according to the first embodiment in theposition and shape of the marking. Other aspects are the same as thefirst embodiment, and hence same explanation will be shortened.

[0068]FIGS. 6A and 6B are a top plan view and a side plan view,respectively, of a lens in the fifth embodiment. As shown in FIG. 6A,the marking 3 b, which is formed on the upper flange surface 21, has aconvex semicylindrical shape protruding toward the center of the lens.The upper surface of the marking 3 b is at the same level as the upperflange surface 21 as shown in FIG. 6B.

[0069] As described above, the lens according to the fifth embodiment ofthis invention has the marking created in the most effective manner toidentify a production jig such as a cavity and a mold. It therebyprovides the same advantage as the lens according to the aboveembodiments.

[0070] The convex shape protruding toward the center of the lens is notnecessarily semicylindrical, and it may be triangular, quadrilateral,and so on.

[0071] Embodiment 6

[0072] A lens according to the sixth embodiment of this invention hasthe same shape as the lens according to the first embodiment. Thisembodiment uses inserts as some of the mold members to produce the lens.Other aspects are the same as the first embodiment, and therefore sameexplanation will be shortened.

[0073]FIG. 7 is a side plan view of a lens according to the sixthembodiment of this invention. Inserts 51 and 52 are also shown therein.The inserts 51 and 52 are mold members to shape a portion including anoptical functional part of the lens 1. Members 53 and 54 are moldmembers to shape the flange part 2. The mold members 53 and 54 are madeseparately from the inserts 51 and 52. On each side, mold members 51 and53, or 52 and 54 form each side of mold part. When assembled, those moldmembers form a mold cavity, in which resin material is injected andmolded. For the lens surface without marking, use of the insert may beeliminated. Specifically, the insert 52 may not be separated from butintegrated to the mold member 54.

[0074] As known from the description, the optical functional part meansthe aperture of the luminous flux that actually passes through the lens,which differs according to use. For example, NA=0.45 for CD, NA=0.60 forDVD, and NA=0.85 for Blu-ray disc. The optical functional part is placedin the inner part of the lens surface.

[0075] A parting line that separates the inserts 51 and 52 from othermold members is somewhere between the outermost periphery of the opticalfunctional part of the lens and the innermost periphery of the markingsurface. Preferably, the parting line is at the inner peripheral area ofthe flange part 2. This is for the reasons including the following. Thefirst is that, even if flash, which is a sharp protrusion, is formed asresin solidifies at the boundary between the inserts 51 or 52 and othermold members, it causes no problem provided it is less than the depth ofthe depressed part. The second reason is that, if the parting line is atthe boundary between the upper flange surface 21 and the lens surface,it is difficult to apply a mirror finish to the upper flange surface 21.

[0076] The mold member 53 has a portion to define the shape of a markingat the part facing the upper flange surface 21 of the flange part. Thisportion allows forming the marking 3 b on the flange surface byinjection molding.

[0077] As described above, the insert 51 is placed in the mold to shapethe optical functional part mainly. This is to facilitate the adjustmentin the production of the lens 1. When producing the lens 1, a marking isintegrally molded on the upper flange surface. It is thus preferred thatthe mold members for the optical functional part can rotate along theoptical axis without changing the position of the mold members for theflange part, which has the cavity number or other marking. The use ofthe inserts 51 eliminates the need to create another united molding partfor a marking on the flange part additionally.

[0078] For example, if the lens produced with the insert placed at acertain position turns out to be poor in quality, the lens can bereproduced after rotating the insert. The position of the insert isrepeatedly adjusted until the lens quality improves.

[0079] In this embodiment, each of the mold members 53 and 54 may becomposed of two or more pieces.

[0080] The present invention places a marking not on the opticalfunctional part but on the other part of the lens. This is especiallysuitable for the manufacturing method that uses the inserts 51 and 52 asthe mold parts to shape the optical functional part. Since the insert 51is a separate part from the mold member 53, it reduces the risk ofdamaging the insert 51 during the process of forming a shapecorresponding to a desired marking on the mold member 53.

[0081] Embodiment 7

[0082] A lens according to the seventh embodiment of this invention isdifferent from the lens according to the first embodiment in the shapeof the marking. Other aspects are the same as the first embodiment, andhence an explanation will be omitted.

[0083]FIG. 8A is an enlarged sectional view of the flange part of thelens according to the fourth embodiment of the invention. FIG. 8B is asectional view showing the above lens placed in the mold parts includingthe inserts 51 and 52. As shown therein, the marking 3 b is a half-roundconcave shape formed on the upper flange surface 21. Since the marking 3b is depressed below the upper flange surface 21, it does not touch thesurface where the lens is placed during the production process. Further,it does not touch an optical recording medium when the lens 1 is mountedto an optical pickup device. This reduces the risk of damage by abrasionwith the surface or the optical recording medium.

[0084] As shown in the figure, the mold members to shape the opticalfunctional part of the lens 1 are the inserts 51 and 52. The moldmembers to shape the flange part 2, on the other hand, are the moldmembers 53 and 54, which are made separately from the inserts 51 and 52.

[0085] Embodiment 8

[0086] The eighth embodiment of this invention relates to an opticalpickup device having the lens according to one of the first to seventhembodiments.

[0087]FIG. 9 shows the structure of an optical pickup device 100 wherethe lens 1 is mounted. The lens 1 is fixed at four points with thepickup holder 4. Specifically, the flange part 2 of the lens 1 isattached to the pickup holder 4 with an adhesive.

[0088] The marking on the flange part 2 is visible to the eye with orwithout a hand lens when the lens 1 is mounted on the optical pickupdevice 100. For a lens with a certain defect, its production process canbe tracked using the marking to identify a production jig, mold,production line process, production place, producer, and so on.

[0089] Another Embodiment

[0090] The lens according to the present invention may be a meniscuslens with one side convex and the other concave, for example.

[0091] From the invention thus described, it will be obvious that theembodiments of the invention may be varied in many ways. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention, and all such modifications as would be obvious to one skilledin the art are intended for inclusion within the scope of the followingclaims.

What is claimed is:
 1. A plastic lens produced by injection molding ofresin material, comprising: a flange part on a periphery of a lenssurface, a flange surface on at least one side of the flange part havinga part higher than the lens surface and a depressed part formed on atleast a part thereof; and a marking integrally molded by injectionmolding to a marking surface of the depressed part, a highest point ofthe marking being lower than a highest point of the flange surface.
 2. Aplastic lens according to claim 1, wherein the flange part has a cutoutportion in an outer side surface thereof.
 3. A plastic lens according toclaim 1, wherein the flange surface is mirror-finished at least in avicinity of an area where the marking is formed.
 4. A plastic lensproduced by injection molding of resin material, comprising: a flangepart on a periphery of a lens surface, a flange surface on at least oneside of the flange part having a part higher than the lens surface; anda marking integrally molded to the flange surface by injection molding,for identifying a production jig used to produce the lens.
 5. A plasticlens according to claim 4, wherein a highest point of the marking islower than a highest point of the flange surface.
 6. A plastic lensaccording to claim 4, wherein the marking is formed in a depressed partof the flange surface.
 7. A plastic lens according to claim 4, whereinthe flange part has a cutout portion in an outer side surface thereof.8. A plastic lens according to claim 4, wherein the flange surface ismirror-finished at least in a vicinity of an area where the marking isformed.
 9. An optical pickup device having the lens according toclaim
 1. 10. An optical pickup device having the lens according to claim4.
 11. A method of manufacturing a plastic lens produced by injectionmolding of resin material in a mold cavity, the lens having a marking ona different part from an optical functional part, comprising the stepsof: providing a mold part for one side comprising a first mold memberand a second mold member, the first mold member and the second moldmember forming a part of the mold cavity; providing a mold part forother side to form the mold cavity cooperable with the mold part for oneside when assembled; injecting resin material into the mold cavity;forming the optical functional part of one side of the lens, with thefirst mold member; and forming the different part of one side of thelens than the optical functional part and the marking thereon, with thesecond mold member.
 12. A method of manufacturing a plastic lensaccording to claim 11, wherein the different part of one side of thelens than the optical functional part comprises a flange part on aperiphery of a lens surface, and a boundary between the first moldmember and the second mold member is located near an innermost peripheryof the flange part of the lens.
 13. A method of manufacturing a plasticlens according to claim 11, wherein the different part of one side ofthe lens than the optical functional part comprises a flange part on aperiphery of a lens surface, and a flange surface of the flange part ofthe lens comprises a depressed part on at least a part thereof and amarking integrally molded to the depressed part by injection molding.14. A method of manufacturing a plastic lens according to claim 11,wherein the different part of one side of the lens than the opticalfunctional part comprises a flange part on a periphery of a lenssurface, and the flange part of the lens comprises a flange surface onat least one side thereof, the flange surface having a part higher thanthe lens surface and a depressed part on at least a part thereof, and amarking integrally molded by injection molding to a marking surface ofthe depressed part, a highest point of the marking being lower than ahighest point of the flange surface.
 15. A method of manufacturing aplastic pickup lens according to claim 11, wherein the different part ofone side of the lens than the optical functional part comprises a flangepart on a periphery of a lens surface, and a flange surface of theflange part comprises a cutout portion in an outer side surface thereof.16. A method of manufacturing a plastic lens according to claim 11,wherein the different part of one side of the lens than the opticalfunctional part comprises a flange part on a periphery of a lenssurface, and a flange surface of the flange part is mirror-finished atleast in a vicinity of an area where the marking is formed.
 17. A methodof production tracing management of a plastic lens produced by injectionmolding of resin material, comprising the steps of: manufacturing theplastic lens comprising a flange part on a periphery of a lens surface,a flange surface on at least one side of the flange part having a parthigher than the lens surface; and a marking integrally molded to theflange surface by injection molding; and tracing production of the lensby use of the marking formed on the lens.
 18. A method of productiontracing management of a plastic lens produced by injection molding ofresin material, comprising the steps of: manufacturing the plastic lenscomprising a flange part on a periphery of a lens surface, a flangesurface on at least one side of the flange part having a part higherthan the lens surface; and a marking integrally molded to the flangesurface by injection molding, a highest point of the marking being lowerthan a highest point of the flange surface; and tracing production ofthe lens by use of the marking formed on the lens.
 19. A method ofproduction tracing management of a plastic lens according to claim 17,wherein a position of the marking is circumferentially different on theflange surface to distinguish production.
 20. A method of productiontracing management of a plastic lens according to claim 17, wherein themarking is formed in at least one place, and a shape of the marking isdifferent to distinguish production.
 21. A mold for manufacturing aplastic lens produced by injection molding of resin material, the lenshaving a marking on a part different from an optical functional part, amold at a side where a marking will be formed comprising: a first moldmember to form an optical functional part of one side of the lens, and asecond mold member to form a part different from the optical functionalpart of one side of the lens, the second mold member being separatablefrom the first mold member and having a portion to form the marking.